In this latest blog from our sustainable materials series we take a closer look at silicone, its practical applications and sustainability credentials:
What is silicone?
Silicones are polymers, which are large molecules composed of many repeated sub-units. These polymers are made up of siloxane – a chain of alternating silicon atoms and oxygen atoms frequently combined with carbon and/or hydrogen. Silicon is an element found in sand, where it is extracted from and passed through hydrocarbons. What makes silicone so popular for use in so many products and applications is the wide variety of temperatures it can withstand whilst maintaining its properties and physical structure. Silicone is ideal for use in continuous temperatures as low as -60°C to as high as around 230°C. However, the amount of time spent in extreme temperatures beyond these values is important. Silicone cannot withstand the highest or lowest temperatures for too long.
Silicones have plastic-like properties: flexibility, malleability, clarity, temperature resistance, and water resistance. Like plastic, they can be shaped or formed and softened or hardened into practically anything. Since they're easy to clean, non-stick, and non-staining, they're popular for cookware and kitchen utensils, too. Silicones have many uses in a variety of industries and consumer products. They can be found in aerospace and construction adhesives, coatings, and sealants because they can withstand extreme temperatures and absorb stress. They are used in electronics as sealants because they are moisture, salt, and corrosion resistant. Furthermore, they’re used to house electronics like computers, fax machines, phones, and keyboards for the same reasons.
Silicones are also found in aerosols like furniture polish and in personal care products like deodorants, make-ups, lotions and sunscreens. One household use of silicone you might be most familiar with is bathroom caulk. Silicone is ideal for this application because it is water resistant and antimicrobial.
Are silicones toxic?
While the research indicates that silicones are certainly very stable, they are not completely inert. In other words, there is a possibility of leaching. For example, one study [1] tested the release of siloxanes from silicone nipples and bakeware into milk, baby formula, and a solution of alcohol and water. Nothing was released into the milk or formula after six hours, but after 72 hours in the alcohol solution, several siloxanes were detected. Many experts and authorities consider silicones to be nontoxic and safe for contact with food and drink. For example, Health Canada states: "There are no known health hazards associated with use of silicone cookware. Silicone rubber does not react with food or beverages, or produce any hazardous fumes."
Sustainability of silicone
As we have discussed in some of our previous blogs, the sustainability of a product relies on the sustainability of the different phase of its lifecycle. So let’s take a look at silicone’s phases:
1. Raw Material
Making silicone starts with silica (silicon and oxygen in the form of sand). According to the U.S. Geological Survey, silica resources for most uses are abundant, so the major environmental impacts are derived from mining silica. But silicone rubber uses only a tiny fraction of the silica that is mined each year, so it shares only a small amount of the responsibility for those impacts which the USGS calls “limited” anyway.
2. Production
The making of 1kg of silicone from silica requires 230-235NJ, roughly 63,900 to 65,300 watt hours. The extraction of silicone from silicone dioxide is extremely energy intensive, as silicon dioxide requires large amounts of energy to be broken down. This process also releases carbon dioxide. However in 2017, a new technique was found to reduce the energy used in making silicone, making this process less energy intensive and more sustainable.
3. Use
All silicone cookware sold is made of food grade silicone, meaning the relevant organizations have deemed it safe for its intended use. Silicone rubber is easy to clean, and won’t require harsh, damaging solvents that can pollute the air or water. A distinct advantage of silicone is its durability. Longevity is definitely an eco-asset, but we need to make sure silicone items get passed on, not thrown out.
4. End of Life
Silicone, like plastic, can be recycled multiple times. However, silicone usually has to be sent to a specialized recycling company to be properly recycled. Because of this, many users will simply throw away silicone at the end of its life. When properly recycled, or sent to a company’s take-back program, silicone can be downcycled into an oil that can be used as industrial lubricant, playground mulch, or another lesser product. Because silicone is so durable, it doesn’t easily biodegrade or decompose. While normal plastics break down into dangerous micro plastic pieces that can ingested by wildlife and ocean life, silicone doesn’t break down much at all. This is why it is important to educate the consumers on what are the relative steps to be taken when an item has reached the end of it life.
[1] https://pubmed.ncbi.nlm.nih.gov/22575024/
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